1. Field of the Invention
The present invention relates to a fuel injection valve for use in an internal combustion engine such as a Diesel engine, and more particularly to a swirl injection valve for injecting a liquid in the form of fine particles.
2. Description of the Prior Art
In the injection valve of this kind, generally speaking, a needle valve is made axially movable within a through hole formed in the body of the injection valve so that the nozzle port formed at the leading end of the through hole is shut off by the needle valve, thereby to inject a liquid under pressure from the nozzle port when the needle valve is moved in the valve opening direction. This injection valve is divided into a first type, in which the needle valve has its leading end formed into a conical valve member to be seated on a frusto-conical valve seat formed at the upstream side of the nozzle port, or a second type, in which the nozzle port is formed at the center of a diaphragm formed at the leading end portion of the body of the injection valve so that the valve member formed at the leading end of the needle valve is forced into a seated position upon the diaphragm. According to these injection valves, however, it is quite difficult to improve the liquid atomizing characteristics and to prevent the liquid from dropping when the valve is closed, merely by changing the shape of the needle valve.
In an improved type of the prior art, the atomizing characteristics, e.g., the distributions of droplets size, diameter, surface area, weight and volume, and the mean droplet diameter relative to those distributions are well known to be good if a swirl liquid flow is established during the liquid injection around the center axis of the needle valve so that the liquid may be injected under a high pressure from the nozzle port. With reference to FIGS. 1 to 5, there is shown a swirl injection valve according to the known concept, in which a swirl chamber is formed within the body of the injection valve upstream of the seating portion between the needle valve and its valve seat.
FIGS. 1 to 3 show a swirl injection valve for intermittently injecting a fuel. In this injection valve, a nozzle port 3 is formed at the leading end portion of the through hole 2 which is formed in the body 1 of the injection valve, and a frusto-conical valve seat 4 is formed at the upstream side of the nozzle port 3. A needle valve 6, which is formed with a conical surface 5 to be seated on the valve seat 4, is axially slidably fitted in the through hole 2. Thus, when the conical surface 5 of the needle valve 6 is seated upon the valve seat 4, the injection of the liquid is interrupted (as shown in FIG. 1.) On the other hand, when the needle valve 6 is moved in the opening direction, the liquid is injected from the nozzle port 3. In the nozzle body 1, moreover, the through hole 2 is expanded upstream of the valve seat 4 to form a pressure chamber 7 between the body 1 and the needle valve 6 being seated upon the valve seat 4. A communication passage 9 for supplying a liquid from a liquid passage 8 into the pressure chamber 7 is opened into the pressure chamber 7 tangentially of the circumference thereof (as shown in FIG. 2). When the injection valve thus constructed has its needle valve 6 moved in its opening direction, the liquid is fed from the liquid passage 8 through the communication passage 9 to the pressure chamber 7 in the tangential direction to the chamber circumference so that it flows down while accomplishing the swirling (or spiral) motions within the pressure chamber 7 and the swirl chamber 10, which is formed between the valve seat 4, downstream of the pressure chamber 7, and the needle valve 6, until it is injected from the nozzle port 3 (as shown in FIG. 3).
In an intermittent type swirl injection valve shown in FIGS. 4 and 5, on the other hand, that portion of the through hole which is downstream of the pressure chamber 7 connected to the liquid passage 8 and upstream of the frustoconical valve seat 4, is formed into a cylindrical surface 11. The needle valve 6 is formed with a cylindrical surface 13 which is formed between the conical surface 5 at the leading end thereof and a conical surface 12 at the upstream side so that it is hermetically fitted in the cylindrical surface 11. There is formed in the surface of the needle valve 6 thus constructed a spiral groove 14 which is started from the upstream side conical surface 12 to pass through the cylindrical surface 13 and over the boundary between the surface 13 and the conical surface 5 at the leading end until it reaches a position upstream of the seated portion of the surface 5 upon the valve seat 4. According to the swirl injection valve thus constructed, while the needle valve 6 is being seated upon the valve seat 4, the downstream end of the spiral groove 14 is shut off by the seating operation of the conical surface 5 thereby to interrupt the injection of the liquid. On the contrary, when the needle valve is moved in its opening direction, the liquid from the pressure chamber 7 flows down along the spiral groove 14 through the clearance between the needle valve 6 and the inner wall of the through hole 2 so that it is injected from the nozzle port 3 (as shown in FIG. 5) while swirling (spirally) within the swirl chamber 10 which is formed between the valve seat 4 and the leading conical surface 5 of the needle valve 6.
In the swirl injection valve having the construction shown in FIGS. 1 to 3, the formation of the communication passage 9 tangentially of the circumference of the pressure chamber 7 is accomplished by forming a bore from the outside of the nozzle body 1 through the liquid passage 8 and by hermetically forcing a plug 15 into the bore at the outer portion of the body 1. In the case of the injection valve having such construction, the communication passage 9 is so relatively short that the pressure loss can be held at a low level. If there exist fine powder dusts in the liquid to be injected, especially, the fuel for a Diesel engine, they are liable to be deposited at a region from the trailing end of the liquid passage 8 to the communication passage 9. In case the deposition of the powder dusts proceeds, it becomes necessary to extract the plug 15 and to clear the deposited dusts, but the extraction of the plug 15 is not easy.
In the swirl injection valve having the construction shown in FIGS. 4 and 5, on the other hand, the cleaning operation of the spiral groove 14 can be accomplished without difficulty by extracting the needle valve 6 itself. In the injection valve of this type according to the prior art, however, the spiral groove 14 has both ends formed, respectively, in the leading end conical surface 5 constituting the seat surface of the needle valve 6 and the upstream side conical surface 12 and has its major portion formed in the cylindrical surface 13 having a reduced diameter at the leading end portion of the needle valve 6. As a result, since the effective area of the spiral groove 14 is small and since the spiral groove itself is formed more than 360 degrees about the center axis of the needle valve 6 according to the designing requirement, the pressure loss when a liquid flows at a high speed through the spiral groove is much higher than that for the construction shown in FIGS. 1 to 3.
On the other hand, there is a spill type swirl injection valve, in which a liquid is fed from its supply source through a supply passage to a swirl chamber thereby to establish a swirl flow around the valve member of the needle valve, while partly spilling the liquid through a spill passage to the supply source, thereby to establish the swirl flow in the swirl chamber at all times. Thus, the liquid forming the swirl flow is injected from a nozzle port when the needle valve is moved in its opening direction to bring its valve member apart from the valve seat. The conventional injection valve of this type has the disadvantages that the machining of the fuel supply passage in the restricted portion at the leading end of the nozzle body in a manner to establish a sufficient swirl flow in the swirl chamber is extremely difficult. Also, the assembling and cleaning operations are difficult. Further, the fuel flow rate and the fuel spray angle cannot be freely selected with ease.